LABORATORI NAZIONALI DI FRASCATI www lnf infn it
LABORATORI NAZIONALI DI FRASCATI www. lnf. infn. it The µ-RWELL: from R&D to industrialization G. Bencivenni (a), P. De Simone(a), G. Felici(a), M. Gatta (a), G. Morello (a), A. Ochi (b) M. Poli Lener (a) LNF-INFN, Frascati-Italy, (b) Particle Physics Group, Department of Physics, Kobe University, Kobe, Japan G. Bencivenni, LNF-INFN 1
OUTLINE q WP 7: Muon detectors for future colliders q Why a new MPGD q The µ-RWELL: description and principle of operation q Detector industrialization: Low-rate vs High-rate layout q Summary G. Bencivenni, LNF-INFN 2
Muon Detectors for future colliders q The future colliders (CEPC, Spp. C and FCC – hh) requires for extremely large muon detectors : q ~10000 m 2 in the barrel q 3 -5000 m 2 in the endcap q 300 m 2 in the very forward region q The detectors have to be operated in high background (very large uncertainties depending on shielding, actual structure, etc. ): q O(1 – 10 k. Hz/cm 2) in the barrel q O(10 – 100 k. Hz/cm 2) in the end-cap q O(1 MHz/cm 2) in the forward region q Taking into account the surface and the expected rates gaseous detectors and in particular MPGDs is the natural solution (straight-forward for CEPC, requiring a significant R&D for the harsher conditions of Spp. C & FCC-hh) q R&D for HL-LHC (CMS & LHCb phase-2 muon upgrade) is clearly a good starting point G. Bencivenni, LNF-INFN 3
Why a new MPGD The R&D on µ-RWELL is mainly motivated by the wish of improving the stability under heavy irradiation & simplify as much as possible construction/assembly procedures G. Bencivenni, LNF-INFN 4
The µ-RWELL architecture The µ-RWELL detector is composed by two elements: the cathode and the µ-RWELL_PCB Drift/cathode PCB The µ-RWELL_PCB is realized by coupling: 1. a “suitable WELL patterned kapton foil as “amplification stage” Copper top layer (5µm) 2. a “resistive stage” for the discharge suppression & current evacuation: Well pitch: 140 µm Well diameter: 70 -50 µm Kapton thickness: 50 µm DLC layer (0. 1 -0. 2 µm) 2 R 50 -200 MΩ/□ i. “Low particle rate” (LR) < 100 k. Hz/cm : 1 single resistive layer surface resistivity ~100 M /� (CMS-phase 2 upgrade – SHIP muon device @ CEPC) Rigid PCB readout electrode 2 3 µ-RWELL PCB ii. “High particle rate” (HR) ≥ 1 MHz/cm 2: more sophisticated resistive scheme must be G. Bencivenni et al. , 2015_JINST_10_P 02008 implemented (MPDG_NEXT- LNF & LHCbmuon upgrade muon device @ Spp. C & FCC-hh) Global detector thickness < 1 cm 3. a standard readout PCB G. Bencivenni, LNF-INFN 5
Principle of operation top copper layer A voltage 400 -500 V between the top copper layer and the grounded resistive kapton foil, generates an electric field of ~100 k. V/cm into the WELL which acts as multiplication channel kapton HV r t The charge induced on the resistive foil is dispersed with a time constant, RC, determined by v the surface resistivity, v the capacitance per unit area, which depends on the distance between the resistive foil and the pad readout plane, t v the dielectric constant of the kapton, r [M. S. Dixit et al. , NIMA 566 (2006) 281] q The main effect of the introduction of the resistive stage is the suppression of the transition from streamer to spark by a local voltage drop around the avalanche location. q As a drawback, the capability to stand high particle fluxes is reduced, but an appropriate grounding of the resistive layer with a suitable pitch solves this problem (High Rate scheme) G. Bencivenni, LNF-INFN 6
Main features of the µ-RWELL The µ-RWELL is a spark protected detector and it is characterized by a simple construction/assembly procedure: q only two components µ-RWELL_PCB + cathode q no critical & time consuming assembly steps: ü no gluing ü no stretching ü easy handling q no stiff & large frames q suitable for large area with PCB splicing technique w/SMALL DEAD ZONE cost effective: q 1 PCB r/o, 1 µ-RWELL foil, 1 DLC, 1 cathode and low man-power easy to operate: q very simple HV supply 2 independent channels or a trivial passive divider (3 GEM detector 7 HV channels) G. Bencivenni, LNF-INFN 7
The µ-RWELL performance: Lab Tests G. Bencivenni, LNF-INFN 8
Detector Gain prototypes with different resistivity (12 -80 -880 M /☐) have been tested with an X-Ray gun (5. 9 ke. V), with Ar/i. C 4 H 10= 90/10 gas mixture, and characterized by measuring the gas gain in current mode. Ar/ISO=90/10 WELL kapton thickness = 50µm 70 50 55 50 70 30 G. Bencivenni, LNF-INFN 9
Rate capability vs layer resistivity Ar/ISO =90/10, G = 2000 – point-like irradiation test with X-ray the gain decrease is correlated with the voltage drop due to the resistive layer solution grounding by “through-vias with a suitable pitch” GEM detector rate(*) . i. rm fo × p. 7 with a 1× 1 cm 2 grounding pitch µ-RWELL & a resistivity of ≈10 M /☐, a rate capability >> 1 MHz/cm 2 can be achieved fulfilling the LHCb requirement (*) Bellazini et al. NIMA 423 (1999) 125 Sauli et al. , NIMA 419 (1998) 410 G. Bencivenni, LNF-INFN a re-scaling with the right gain of 4000 would be required rate for a drop G = -3% 10 10
Discharges: µ-RWELL vs GEM test with X-ray µ-RWELL Discharge Amplitude (n. A) single-GEM Ar/CO 2 = 70/30 the µ-RWELL detector reaches discharge amplitudes of few tens of n. A, <100 n. A @ max gain the single-GEM detector reaches discharge amplitudes of ≈ 1µA (of course the discharge rate is lower for a triple-GEM detector) More quantitative studies must be performed G. Bencivenni, LNF-INFN 11
The µ-RWELL performance: Beam Tests H 4 Beam Area (RD 51) Muon beam momentum: 150 Ge. V/c Goliath: B up to 1. 4 T BES III-GEM chambers -RWELL prototype 12 -80 -880 MΩ /□ 400 µm pitch strips APV 25 (CC analysis) Ar/i. C 4 H 10 = 90/10 RWELL = (52+-6) µm @ B= 0 T after TRKs contribution subtraction GEMs Trackers G. Bencivenni, LNF-INFN 12
Space resolution: orthogonal tracks is alys n a C C Ar/ISO=90/10 The space resolution exhibits a minimum around 100 MΩ/□. At low resistivity the charge spread increases and then σ is worsening. At high resistivity the charge spread is too small (Cl_size 1) then the Charge Centroid method becomes no more effective (σ pitch/ 12). G. Bencivenni, LNF-INFN 13
The two detector layouts (I) High Rate Low Rate q single resistive layer with “edge detector” grounding q double resistive layer with “through vias” grounding with a O(1 cm 2) pitch q “ 2 D” current evacuation q “ 3 D” current evacuation q “large current path to ground” higher resistance to ground large Voltage drop spread large gain non-uniformity low rate < 100 k. Hz/cm 2 q “short current path to ground” lower resistance to ground small Voltage drop spread small gain non-uniformity high rate ≥ 1 MHz/cm 2 q implementation: kapton foil + PCB coupling q implementation: multi-layer flex w/through-vias + PCB coupling q R&D completed(*), engineering on -going q R&D almost completed(*), engineering ready to be started (*)WELL shape/geometry as well as the 2 D readout still to be studied in details G. Bencivenni, LNF-INFN 14
Towards detector industrialization Low-Rate layout G. Bencivenni, LNF-INFN 15
The µ-RWELL_PCB for Low Rate (CMS/SHi. P) Copper layer 5 µm 1 Kapton layer 50 µm DLC layer: 0. 1 -0. 2 µm (50 -200 M /�) DLC-coated kapton base material 2 Pre-preg (50 µm) epoxy – film PCB (1 -1. 6 mm) 3 DLC-coated base material after copper and kapton chemical etching (WELL amplification stage) G. Bencivenni, LNF-INFN 16
Towards detector industrialization (I) LR scheme (LARGE AREA) In the framework of the CMS-phase 2 muon upgrade we are developing large size µRWELL. The R&D is performed in strict collaboration with Italian industrial partners (ELTOS & MDT). The work will be performed in two years with following schedule: 1. Construction & test of the first 1. 2 x 0. 5 m 2 (GE 1/1) µ-RWELL 2. Mechanical study and mock-up of 1. 8 x 1. 2 m 2 (GE 2/1) µ-RWELL 3. Construction & test of the first 1. 8 x 1. 2 m 2 (GE 2/1) µ-RWELL ~40 times larger than small protos !!! 2016 12/2017 - 6/2018 ~300 times larger than small protos !!! 45 0 Splicing zone < 0. 5 mm wide 1200 mm G. Bencivenni, LNF-INFN Four PCB µ-RWELL spliced with the same technique used for large ATLAS MM + only one cathode closing the detector 1. 8 x 1. 2 m 2 (GE 2/1) µ-RWELL 1. 2 x 0. 5 m 2 (GE 1/1) µ-RWELL 17
Towards detector industrialization (III) (LR scheme) The µ-RWELL manufacturing steps Present Next Future (? ) Detector design: LNF – Italy DLC sputtering: Be-Sputter – Japan PCB manufacturing: ELTOS – Italy PCB – Kapton foil gluing: MDT – Italy PCB – Kapton gluing: ELTOS – Italy Cu/kapton etching: Rui’s Work. – CERN Cu/kapton etching: ELTOS – Italy (*)ELTOS or another Company able to work on flex substrates G. Bencivenni, LNF-INFN 18
Readout-PCB production @ ELTOS ü GE 1/1 – PCB-readouts manufatured at ELTOS 1, 2 m 0, 5 m G. Bencivenni, LNF-INFN 19
DLC sputtering on Kapton foils ü DLC sputtering on large Kapton foils (w/copper on one side) completed @ Be. Sputter Co. , Ltd (Japan) Average Surface Resistivity M /� Foil 1 (800 A) Foil 2 (1300 A) Foil 3 (1800 A) Foil 4 (1500 A) Foil 5 (1500 A) 433± 90 68± 9 41± 12 122± 22 180± 17 Ar/ISO=90/10 G. Bencivenni, LNF-INFN 20
Coupling the DLCed Kapton with r/o-PCBs ü gluing the DLCed foils on the readout–PCBs @ MDT (Milano) G. Bencivenni, LNF-INFN 21
Final etching and detector closing 1 – final etching @ CERN w/problems 2 – closing a detector (@LNF) with a spare DLCed kapton foil etched @ CERN Copper Delamination 3 - The detector tested at H 8 -Sp. S beam line (CERN) together with two small high rate µ-RWELLs G. Bencivenni, LNF-INFN 22
The High Rate µ-RWELL G. Bencivenni, LNF-INFN 23
LHCb-muon Requirements @ 2× 1034 cm-2 s-1 ü Rate up to 3 MHz/cm 2 with an additional filter in front of M 2 ü Efficiency for single gap > 95% within a BX (25 ns) ü Long stability up to 6 C/cm 2 accumulated charge in 10 y of operation ü Pad cluster size < 1. 2 Expected max rate MHz/cm 2 (*) Active area cm 2 Pad Size cm 2 (*) Rate/Pad MHz # pad/gaps #chambers (with 2 gaps) M 2 R 1 3 30 x 25 0. 63 x 0. 77 1. 5 1536 24 12 M 2 R 2 0. 5 60 x 25 1. 25 x 1. 58 1 768 48 24 M 3 R 1 1 32. 4 x 27 0. 67 x 1. 7 1 768 24 12 M 3 R 2 0. 15 64. 8 x 27 1. 35 x 3. 4 0. 7 384 48 24 (*) average rate is about 50% of maximum rate (*) X, Y/4 w. r. t. present logical pads in M 2 R 1 -R 2; a factor 2 more in Y, to halve the rate/Pad X, Y/2 w. r. t. present logical pads in M 3 R 1 and M 3 R 2 Same particle flux as expected at future hadron colliders 24
The µ-RWELL_PCB for High Rate (LHCb) Copper layer 5 µm 1 Kapton layer 50 µm DLC layer: 0. 1 – 0. 2 µm (50 – 200 M /�) 2 2 nd resistive kapton layer with ∼ 1/cm 2 “through vias” density DLC-coated kapton base material 3 2 nd resistive kapton layer insulating layer pad/strips (9 -18 µm thick) readout on standard PCB (1 – 1, 6 mm) “through vias” for grounding 4 DLC-coated base material after copper and kapton chemical etching ( WELL amplification stage) G. Bencivenni, LNF-INFN 25
Industrialization of the HR layout The HR layout requires for a double kapton layer sandwich: v the first layer acts as amplification stage and first resistive layer v the second layer as second resistive layer for grounding The two resistive layers must be connected one to each other by means a pattern of through-vias (~1 cm 2 pitch) The second resistive layer is allows a safe grounding through the readout electrodes by means conductive-vias (~1 cm 2 pitch) The other component is the readout board, a standard PCB on FR 4 substrate The industrialization of such a version of µ-RWELL clearly requires for a Company able to work on both flexible and rigid substrates G. Bencivenni, LNF-INFN 26
The µ-RWELL performance: small vs large proto (very preliminary) G. Bencivenni, LNF-INFN 27
Ve ry pr eli m in ar y Large vs Small proto TB results G. Bencivenni, LNF-INFN 28
Future Programs q Consolidation of the engineering program of the singleresistive layer layout with industrial partners: ELTOS – MDT + Rui – CERN (flex photolithography) (2017 – 2018) (activity already financed by RD-phase 2) q Starting of the engineering phase of the double-resistive layer layout, with industrial partners: ELTOS + TECHTRA (flex photolithography) (2017 -2019) (financial request for the 2017 10 k€) G. Bencivenni, LNF-INFN 29
Summary The µ-RWELL is a compact, simple to assemble & suitable for large area, MPGD: o gas gain ∼ 104 o intrinsically spark protected o rate capability > 1 MHz/cm 2 o space resolution < 60µm R&D & engineering (with industrial partners) o large area w/LR scheme (up to 2 m 2 - CMS, SHi. P) is ongoing with very interesting results o medium area w/HR scheme (< 0. 4 m 2 – LHCb) is going to be started o R&D on large gain WELL amplification stage & 2 D readout G. Bencivenni, LNF-INFN 30
SPARE SLIDES G. Bencivenni, LNF-INFN 31
GEM vs RWELL etching GEM Single mask RWELL Single mask Kaneka base material DLC Hole patterning in Cu Polyimide etch Bottom electro etch (cathode protection) Second Polyimide Etch G. Bencivenni, LNF-INFN 32
Cathodic Protection 0 V +3 V An example of active corrosion protection CP is a technique to control the corrosion of a metal surface by making it work as a cathode of an electrochemical cell. Used to protect ship hulls and oil pipes Resist layer to protect back part from the bath Bath at +3 V Bottom electrode at +3 V is chemically etched Top electrode at ground is electrically protected G. Bencivenni, LNF-INFN 33
The two detector schemes (II) Single layer d d’ Double layer (1 cm) d’ upper layer d (50 cm) r bottom layer (*) point-like irradiation Ω ~ ρs x d/2πr Ω’ ~ ρs’ x d’/πr Ω/ Ω’ ~ (ρs / ρs’) x d/2 d’ If ρs = ρs’ Ω/ Ω’ ~ d/2 d’ = 25 (*) Morello’s model: appendix A-B (G. Bencivenni et al. , 2015_JINST_10_P 02008) G. Bencivenni, LNF-INFN 34
GEMs: stability The biggest enemy of MPGDs are the discharges due to the fine structure and the typical micrometric distance between their electrodes, the occasional occurrence of heavily ionizing particles may trigger local breakdowns that can eventually damage the detector and/or the related readout electronics GEM 241 S. Bachmann et al. , NIMA A 479(2002) 294 Am souce G. Bencivenni, LNF-INFN with multiple structures the discharge probability is strongly reduced but not completely suppressed 35
GEM detector currently running @ HEP Experime nt Instrum ented area (m 2) Gas Mixture Gain Flux HV-type 2 (MHz/cm ) # lost sector for shorts COMPASS 2 LHCb % damaged area Front-End Electronics Ar/CO 2 4000 <1 HV passive divider ? ? ? 0. 6 Ar/CO 2/CF 4 8000 1 HV active divider 5 (All on GEM #1) 1% CARIOCA -GEM TOTEM 0. 6 Ar/CO 2 8000 <1 HV passive divider 6 percent level VFAT 2 KLOE 2 4 Ar/i-C 4 H 10 12000 0, 01 7 independent ch; then active divider 61 5% (8 GEM#1, 28 GEM#2, 25 GEM#3) APV 25 GASTONE A damaged GEM sector could required for the replacing of a whole a detector gap !! G. Bencivenni, LNF-INFN 36
GEMs: the construction challenge LHCb-LNF/Ca The construction of the GEM requires some assembly steps such as the stretching of the 3 GEM foils, with a quite large mechanical tension to cope with 1 kg/cm. Improvements in the GEM construction process has been recently introduced by R. de Oliveira (NS 2 detector assembly scheme): no gluing, no soldering, no spacer in the active area re-opening of the detector if repairs needed became possible. But the GEM construction still remains a demanding & complex operation requiring delicate stretching with specialized man-power. O-ring GND Anode electrode NS 2(CERN): no gluing but still stretching … Free to slide GND Drift electrode External screws to adjust stretching G. Bencivenni, LNF-INFN Embedded nut GEM attaching structure (4 pieces defining gaps) 37
The µ-RWELL vs GEM (Garfield simulation) GEM – Ar: CO 2 70: 30 gas mixture Signal from a single ionization electron in a GEM. The duration of the signal, about 20 ns, depends on the induction gap thickness, drift velocity and electric field in the gap. Signal from a single ionization electron in a µ-RWELL. The absence of the induction gap is responsible for the fast initial spike, about 200 ps, induced by the motion and fast collection of the electrons and followed by a ~50 ns ion tail. µ-RWELL – Ar: CO 2 70: 30 gas mixture G. Bencivenni, LNF-INFN 38
GE 1 -1 µ-RWELL etching @ CERN The final copper/Kapton etching done @ CERN v the etching on small DLC samples was perfect: after 10 minutes the holes were around 50 microns. v the etching on the CMS µ-RWELL was not good: during the kapton etching, the copper started to delaminate after 2 min, which means that copper adherence has been compromised: the ELTOS, by mistake, has “scratched” the surface (in a “sanding-machine”, just after the MDT pressing) and the copper adhesion on the kapton has been damaged. Copper Delamination Rui is trying to solve the problem as follows: i. mechanically polishing one of the PCB in order to remove the kapton and the pre-preg down to the metal strips level (recovering one PCB) ii. etching a spare DLCed kapton foil (not damaged by ELTOS – glued on a pre-preg support last June) iii. gluing the DLCed kapton foil on the recovered PCB (@ LNF by vacuum bag tech. ) G. Bencivenni, LNF-INFN 39
Muon System upgrade phase – 1 b & beyond LS 3: phase-1 b new, high rate, muon chambers for busy regions LS 4: phase-2 luminosity upgrade at ~2 x 1034 cm-2 s-1 muon detector response at 2× 1034 cm-2 s-1 is seriously affected by the increased rate profit of the very long shutdown LS 3 to consolidate our Muon System with new chambers in the innermost regions design and technology must face the luminosity upgrade of phase-2 new shielding to reduce the rates on M 2, we do expect a rate reduction of ≈ 50% new pads detectors in M 2 R 1, M 3 R 1 (and M 2 R 2, M 3 R 2) pad size X, Y/2 w. r. t. present logical pads detailed MC studies must be done to define the final configuration IB removal this would allow to cancel the ghost pads rate G. Bencivenni, LNF-INFN 40
MPGDs: stability The biggest “enemy” of MPGDs are the discharges. Due to the fine structure and the typical micrometric distance of their electrodes, MPGDs generally suffer from spark occurrence that can be harmful for the detector and the related FEE. GEM MM 241 Efficiency discharge probability Strongly reduced but not completely suppressed Efficiency & discharge probability Am souce 10 Ge. V/c proton S. Bachmann et al. , NIMA A 479(2002) 294 G. Bencivenni, LNF-INFN A. Bay et al. , NIMA 488 (2002) 162 41
Technology improvement: resistive MPGD For MM, the spark occurrence between the metallic mesh and the readout PCB has been overcome with the implementation of a “resistive layer” on top of the readout itself. The principle is the same as the resistive electrode used in the RPCs: the transition from streamer to spark is strongly suppressed by a local voltage drop. The resistive layer is realized as resistive strips capacitive coupled with the copper readout strips. voltage drop due to sparking G. Bencivenni, LNF-INFN 42
MPGDs: the challenge of large area A further challenge for MPGDs is the large area: NS 2(CERN): no gluing but still stretching … Ø the construction of a GEM requires some time-consuming (/complex) assembly steps such as: • the stretching of the 3 GEM foils (with quite large mechanical tension to cope with, 1 kg/cm) • the splicing of GEM foils to realize large surfaces is a demanding operation introducing not negligible dead zones (~3 mm). The width of the raw material is limited to 50 -60 cm. Handling of a stretched Ø similar considerations hold for MM: mesh ü the splicing of smaller PCBs is possible, opening the way towards the large area covering (dead zone of the order 0. 3 – 0. 5 mm). • The fine metallic mesh, defining the amplification gap, is a “floating component” stretched on the cathode (~1 kg/cm) and electrostatically attracted toward the PCB Possible source of gain non-uniformity G. Bencivenni, LNF-INFN 43
The two detector layouts (II) single layer d d’ (1 cm)d’ r r double layer upper layer d (50 cm) conductive vias (*) point-like irradiation, r<<d Ω is the resistance seen by the current generated by a radiation incident in the center of the detector cell Ω ~ ρs x d/2πr inferior layer Ω’ ~ ρs’ x d’/πr Ω/ Ω’ ~ (ρs / ρs’) x d/2 d’ If ρs = ρs’ Ω/ Ω’ ~ d/2 d’ = 25 (*) Morello’s model: appendix A-B (G. Bencivenni et al. , 2015_JINST_10_P 02008) G. Bencivenni, LNF-INFN 44
µ-RWELL: B≠ 0 with Ar/ISO=90/10 s i s y CC a l na June 2015 – θ=0°, B= 0 T Dec 2014 – θ=0°, B= 0. 5 T June 2015 – θ=0°, B= 1 T June 2015 - θ=0° For θ=0° and 0 < B < 1 T σ < 180 µm and ε > 98% G. Bencivenni, LNF-INFN 45
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